STP mode question

Answered Question
Nov 23rd, 2008

Guys,

I have two 2960G switches in my DMZ that are running STP 'pvst'

I have read documentation that supports the theory that rapid-pvst is better as it takes considerably less time to converge compared to pvst

I would like to enable this but have a couple of concerns that I cannot find the answers for in any docs and I dont have a lab to test out...

Connected to the DMZ switch is a third party switch. I have no idea what mode this switch is running in and the vendor will not share this information with me. If this switch was running pvst and I enabled rapid-pvst on my switch would this cause any issues??? I cannot afford to lose connectivity to the third party switch as it runs one of our financial market systems.

Can anyone offer an insight into this please?

Thanks,

Darren

I have this problem too.
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Correct Answer by vishwancc about 8 years 1 month ago

Hi Darren,

There are thinks that could be done to minimise the possibility of any flap.

But since there are only 2 vlan ( vlan 1 and 12 ) that you are using in the network no need to change the mode.

But if you are looking for adventure go ahead and enjoy.-)

Chao

Vishwa

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vishwancc Sun, 11/23/2008 - 21:49

Hi Darren,

Is the third part switch cisco.

If yes , what vlans are you passing through the TRUNk to the third party switch.

If we know that give show spanning tree vlan x and show spanning-tree detail and summary we could know which spanning tree is the third party running.

My guess is that if it is cisco there will not be any problem,but there might be connectivty issue when you migrate from pvst to rapid-pvst.

Chao

Vishwa.

darren-carr Sun, 11/23/2008 - 21:55

Hi Vishwa,

The switch to switch relationship is mine is a 2960G and the third party is a 2950.

On my switch the port that connects the two switches is defined as an 'access' port

We have provisioned a vlan for the third party which is VLAN12.

So going between the two switches is only the native vlan (VLAN1) and VLAN12.

If I change the mode of the switch what sort of outage in terms of links dropping should I expect?

Given the limited number of devices I have connected to the switch is it even worth going through the hassle of changing the mode? 60 second convergence time would be acceptable, id like to reduce this but dont want to if there are too many dramas with doing this.

Thanks

Darren

Correct Answer
vishwancc Sun, 11/23/2008 - 22:03

Hi Darren,

There are thinks that could be done to minimise the possibility of any flap.

But since there are only 2 vlan ( vlan 1 and 12 ) that you are using in the network no need to change the mode.

But if you are looking for adventure go ahead and enjoy.-)

Chao

Vishwa

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